The present invention provides p-type group II-VI semiconductor compounds.
As used herein, the group II-VI semiconductor compounds include group II elements selected from zinc, cadmium, the alkaline earth metals such as beryllium, magnesium calcium, strontium, and barium, and mixtures thereof, and group VI elements selected from oxygen, sulfur, selenium, tellurium, and mixtures thereof. The group II-VI semiconductor compounds may be doped with one or more p-type dopant. Such p-type dopants include, but are not limited to, nitrogen, phosphorus, arsenic, antimony, bismuth, copper, chalcogenides of the foregoing, and mixtures thereof. Zinc oxide and zinc sulfide are two presently preferred group II-VI semiconductor compounds.
Zinc oxide (ZnO) and zinc sulfide are wide band gap semiconductors with potential for use in electrically excited devices such as light emitting devices (LEDs), laser diodes (LDs), field effect transistors (FETs), photodetectors operating in the ultraviolet and at blue wavelengths of the visible spectrum, and other similar devices. Gallium nitride (GaN) is becoming more commonly used as a semiconductor material for the electronic devices mentioned above.
Zinc oxide has several advantages over GaN. For instance, ZnO has a significantly larger exciton binding energy than GaN, which suggests that ZnO-based lasers should have more efficient optical emission and detection. Zinc oxide drift mobility saturates at higher fields and higher values than GaN, potentially leading to higher frequency device performance. The cost and ease of manufacture of zinc oxide is attractive when compared to other common semiconductor materials. Zinc oxide has superior radiation-resistance (2 MeV at 1.2×1017 electrons/cm2) compared to GaN, which is desirable for radiation hardened electronics. Zinc oxide has high thermal conductivity (0.54 W/cm·K). Zinc oxide has strong two-photon absorption with high damage thresholds, rendering it ideal for optical power limiting devices. Unlike GaN, zinc oxide does not form polytypes or crystal lattice stacking irregularities.
N-type zinc oxide semiconductor materials are known and relatively easy to prepare, such as ZnO doped with aluminum, gallium, or other known n-type dopants. P-type zinc oxide semiconductor materials are theoretically possible, but have been difficult to prepare. D. C. Look et al., “The Future of ZnO Light Emitters,” Phys. Stat. Sol., 2004, summarize data on p-type ZnO samples reported in the literature. The best reported ZnO samples have resistivity values of 0.5 ohm·cm (N/Ga dopants) and 0.6 ohm·cm (P dopant). Many of the reported p-type zinc oxide samples tend to be light, heat, oxygen, and moisture sensitive. Some convert to n-type material over time. Their stability has been questioned. Some of the more-stable p-type zinc oxide materials reported in the literature are prepared using complex and expensive fabrication processes, such as molecular beam epitaxy. No commercially viable p-type zinc oxide semiconductor materials are currently known. Therefore, it would be an advancement in the art to provide commercially viable p-type zinc oxide semiconductor materials. More particularly, it would be an advancement in the art to provide commercially viable p-type group II-VI semiconductor materials.